kasetsart journal natural science

170
DISCUSSION
The average total ammonia nitrogen was
high in earthen ponds with some shrimp mortalities
(10% of total number) during the 5 th - 9 th week of
culturing. High total suspended solids in earthen
ponds was due to high erosion associated with
aeration and rain. The result of less plankton in
the earthen ponds was a consequence of high total
suspended solids and therefore limited light
penetration for photosynthesis (Boyd, 1990). Moss
(1995) revealed that L. vannamei grew 1.5 to 1.9
times faster if the water had a high algae content,
compared to clean water. A high level of ammonianitrogen
and a low level of natural nutrient were a
major cause of lower production in earthen ponds
compared to lined ponds. This present study result
is similar to the study of Moss (1995) and Pruder
et al. (1992), who reported that L. vannamei
Kasetsart J. (Nat. Sci.) 40(1)
Table 3 Water quality of rearing pacific white shrimp in earthen ponds and ponds lined with
polyethylene.
Parameter Mean ± S.D.
Earthen pond HDPE lined pond
Temperature (°C)
Morning 29.5 ± 0.9 30.0 ± 0.8
Afternoon 30.7 ± 1.0 31.3 ± 1.1
pH
Morning 7.7 ± 0.1 7.7 ± 0.1
Afternoon 8.1 ± 2.1 8.3 ± 0.1
Dissolved oxygen (mg/l)
Morning 4.8 ± 0.7 4.8 ± 0.8
Afternoon 5.9 ± 1.1 6.3 ± 0.8
Salinity (ppt) 4.4 ± 1.0 3.7 ± 0.9
Conductivity (mmhos/cm) 8.1 ± 1.9 6.9 ± 1.6
Alkalinity (mg/l) 142.8 ± 30.3 134.1 ± 28.5
Total ammonia-nitrogen (mg/l)* 0.44 ± 0.40 0.35 ± 0.20
Nitrite-nitrogen (mg/l) 0.61 ± 0.60 0.74 ± 0.64
Hardness (mg/l) 1,113.8 ± 215.1 947.3 ± 224.5
Total suspended solids (mg/l)* 262.0 ± 197.0 98.6 ± 36.0
Chlorophyll a (mg/l) 218.4 ± 137.4 285.3 ± 144.5
Plankton (cell/l)* 2.6×10 6 ± 2.5×10 6 1.6×10 7 ± 3.6×10 4
* It is significantly different at P40% of clay) as lining pond with polyethylene is
rather costly, which is estimated at 30,000 Baht/rai.